Effect of tempering on the corrosion resistance of supermartensitic stainless steels

Supermartensitic stainless steels have been used in the oil and gas industry for onshore and offshore tubing applications, due to their good mechanical properties, weldability and excellent corrosion resistance. They are hardened by quenching heat treatment, and to improve their toughness, are submitted to tempering. During the tempering, some phase precipitation occurs, which depending on the time and temperature parameters, produces some undesired changes in the steel properties. The aim of this research was to study the microstructure and the corrosion resistance of supermartensitic stainless steel in quenched and different tempered conditions (550 degrees C, 600 degrees C and 650 degrees C). At the microstructure of the 650 degrees C tempered sample was observed the formation of austenite and precipitates of chromium, like Cr(3)C(2) and Cr(7)C(3). The polarization curves indicated that the heat treatment influences the anodic behavior, changing the passive region and the passive,film characteristics. The tempering changes the corms ion resistance, decreasing the degree of sensitization when increasing the temperature from 550 degrees C to 650 degrees C, this occurs due to the recovery of the chromium impoverished zones.